OVERHEATED EARTH WILL KILL HUMANS

Reasonable worst-case scenarios for global warming could mean deadly temperatures for humans in coming centuries, according to research findings from Purdue University and the University of New South Wales, Australia.

Researchers have for the first time calculated the highest tolerable wet-bulb temperature and found that it could be exceeded for the first time in human history in future climate scenarios if greenhouse gas emissions continue at their current rate--ultimately reaching temperatures not seen on earth for 50 million years.

Wet-bulb temperature is equivalent to what is felt when wet skin is exposed to moving air. It includes temperature and atmospheric humidity and is measured by covering a standard thermometer bulb with a wetted cloth and fully ventilating it.

The researchers calculated that humans and most mammals, which have internal body temperatures near 37 degrees Celsius, will experience a potentially lethal level of heat stress at a wet-bulb temperature over 35 degrees that continues for six hours or more.

At worst whole countries would intermittently be subject to severe heat stress requiring large-scale adaptation efforts. Livestock would still be exposed. Outside work would be hazardous.

The Intergovernmental Panel on Climate Change estimates of business-as-usual warming by 2100 are 4 degrees Celsius, eventual warming of 14 degrees is feasible.

"We found that a warming of 7 degrees would cause some areas of the world to surpass the wet-bulb temperature limit, and a 12-degree warming would put half of the world's population in an uninhabitable environment. When it comes to evaluating the risk of carbon emissions, such worst-case scenarios need to be taken into account. It's the difference between a game of roulette and playing Russian roulette with a pistol. Sometimes the stakes are too high, even if there is only a small chance of losing."

A person produces 100 watts of heat, which has to be got rid of. If the wet-buld temperature is too high that becomes impossible.

"The wet-bulb limit is the point at which people would overheat even if they were naked in the shade, soaking wet and standing in front of a large fan. Although we are very unlikely to reach such temperatures this century, they could happen in the next."